33. Ancient cultures looked up to the stars, telling each other myths and legends : beautiful starlores . The moral of those tales , over the years survived for mankind . Modern cultures look to the stars too : the era of the high tech eyes explores the universe in another way and will help mankind to survive Enjoy the fascinating world of astronomical spectroscopy Marc Trypsteen

22. At the starting position the sum of both angles is α + β = 90 ° . Depending on the chosen or desired geometry the value of 휶 ± 휷 is a typical parameter of the spectrograph. As a result this total angle between the incident rays at the collimator and the diffracted rays collected by the focuser can be fixed going from 90 ° to a small angle value indicated in Fig. 5.3 from C 90 ° to C Littrow , where C corresponds to type C from Fig. 4.10. The selected configuration influences the overall performance but also the limitations of the spectrograph. Turning the focuser to the left so that the angle to the grating normal becomes β < α , e mpirically improves the spectral resolution. At the endpoint the focuser and the collimator are working together representing the idea of the small angle Littrow configuration ( λ B = 2d sin Θ B in Fig. 4.10 ). Which concept can finally be used depends on the optical design of collimator and focuser, the blaze angle of the grating and the resulting linear dispersion. It depends further on the intended area of astronomical applications. COMPLETE SPECTROSCOPY For AMATEUR ASTRONOMERS 2017 WALKER & TRYPSTEEN